A comparison of the thermal insulation properties of different clothing materials
The hypothesis does not hold true: among the fabrics, wool did not keep the water in the flask warm for the longest period of time.
Ideally, clothes should be comfortable. They must be thermal-resistant in order to protect their wearers from cold weather. In hot climates, people should wear clothes that allow water vapor to pass through. Today, there are many kinds of commercially available, patented fabrics which are light, yet they provide good thermal insulation.
Use other materials such as fur, silk and leather.
Use thicker clothes. How do the results compare?
Clothing - http://en.wikipedia.org/wiki/Clothing
12 tips to help you choose warm clothes - http://www.websiterepairguy.com/articles/household_tips/stay_warm.html
Be careful when handling hot water. An adult is required for the operation of the drill.